Three-dimensional (3D) imaging devices known in the art capture images forming a 3D image (a left eye image and a right eye image) with binocular disparity. The captured images are then reproduced as a 3D image when displayed by a display device that can project images forming a 3D image (a left eye image and a right eye image) separately for the left eye and for the right eye (hereafter such a display device is referred to as a “3D display device”).
The 3D imaging devices can vary in the number of their optical systems and the number of their image sensors. The 3D imaging devices can also use various imaging techniques including the parallel viewing method and the time-sequential (frame-sequential) method. Typical 3D imaging devices can be twin-lens imaging devices, which use two optical systems (an optical system for the right eye and an optical system for the left eye). Some of the twin-lens 3D imaging devices may be designed to change their 3D imaging parameters including the angle formed by the intersection of the optical axes of the two optical systems (the angle of convergence).
Other 3D imaging devices can be single-lens imaging devices that can capture a right image and a left image having a disparity between them (a right eye image and a left eye image) without using two optical systems but by only using a single optical system (refer to, for example, Patent Literature 3). Such single-lens 3D imaging devices perform imaging equivalent to the imaging performed using two cameras that have a small disparity between them, while being based on the same principle as the imaging performed using two cameras (imaging performed using two optical systems).
Still other 3D imaging devices capture two images forming a 3D image (a left eye image and a right eye image) using a single camera (an imaging device) through individual two shots performed at different lateral (horizontal) positions (this technique is hereafter referred to as “two-shot imaging”). The two-shot imaging can be used only for stationary subjects. Also, this technique requires an experienced user who can correctly take two shots while laterally (horizontally) moving the camera. The two-shot imaging is effective because it is simple and allows imaging to be performed with a large binocular distance (hereafter the binocular distance used in imaging is referred to as the imaging SB, the imaging stereo base, the stereo base, or the interaxial). To enable appropriate 3D imaging using this technique, such imaging devices can have an assist function for assisting the image shooting performed manually without using tools including special rigs. The assist function includes displaying of guide information on a liquid crystal display of the camera.
Parallel Viewing Method and Cross-eyed Viewing Method
The imaging devices for capturing and displaying 3D images described above may use the parallel viewing method or the cross-eyed viewing method known in the art.
With the parallel viewing method, two cameras are arranged respectively on the left and on the right. The two cameras are arranged to have their optical axes being parallel to each other. In this state, the cameras capture images forming a 3D image (a 3D video). The imaging SB, or the distance between the two cameras, is set to the interval between the two eyes of a human (about 6.5 cm). The captured images (the left eye image and the right eye image) forming a 3D image are displayed on a screen (a display screen of a display device) at positions electrically distant from each other by the distance equal to the imaging SB. With this parallel viewing method, the images displayed on the screen (on the display screen of the display device) are identical to the images actually viewed at the positions of the cameras when they are captured. Also, the distance to the subject, the size of the subject, and other information captured in the images are reproduced without any changes in the images displayed by the display device. In other words, the parallel viewing method enables “distortionless 3D imaging”.
With the cross-eyed viewing method, two cameras (included in an imaging device) are arranged in a manner that their optical axes form an angle of convergence. With the cross-eyed viewing method, a subject at the point of intersection (the point of convergence) between the optical axes of the two cameras (included in the imaging device) is typically placed on the screen. The subject can also be placed more frontward or more backward by changing the angle of convergence. With this cross-eyed viewing method, a selected subject can be easily placed at a predetermined position. The cross-eyed viewing method can thus be useful in enabling, for example, effective positioning used in movie films, and is widely used in the film industry and other related industries.
However, the 3D imaging and displaying techniques described above can have problems that occur depending on the geometric conditions.
Under certain geometric conditions, a 3D image (video) captured with the above 3D imaging techniques can fail to reproduce natural depth when the image is displayed with the above 3D displaying techniques. More specifically, the depth of the displayed image (specifically a range behind the virtual screen (the display screen)) can have imaging failures under certain geometric conditions. For example, the displayed image may be compressed excessively (unnaturally) or expanded excessively (unnaturally) in the depth direction, or may diverge backward and cannot be fused.
The geometric conditions refer to conditions determined geometrically by the alignments of components responsible for capturing and displaying 3D images during imaging and/or displaying. The geometric conditions can be determined by, for example, the parameters described below:
(A) Parameters during Imaging
(A1) the convergence angle, (A2) the angle of view of the lens(es) or zooming, (A3) the imaging SB, (A4) the focal length, and other imaging parameters
(B) Parameters during Displaying
(B1) the size of the display device (the size of the display screen) and (B2) the viewing distance
Under certain geometric conditions, the images having a disparity between them (the images forming a 3D image) may be captured and displayed inappropriately with the 3D imaging and displaying techniques.
The conditions associated with human vision can also affect the imaging and display performance achieved by the above 3D imaging and displaying techniques. When, for example, an extremely near scene or an extremely far scene is imaged three-dimensionally, the captured images (the images forming a 3D image) will have a disparity between them having a large absolute value. When these captured images (the images forming a 3D image) are displayed by a display device, many viewers would not be able to fuse the images into a 3D image and would perceive them only as a double image (an image that cannot be viewed three-dimensionally). Although such images (the images forming a 3D image) may be viewed three-dimensionally, the resulting 3D image would cause extreme fatigue of the viewers. Due to human vision, such images (images forming a 3D image) may be captured and displayed inappropriately with the above 3D imaging and displaying techniques.
With other techniques proposed to solve the problems, the disparity is detected from the left and right images (the left eye image and the right eye image), and the disparity adjustment is performed based on the detected disparity. This would enable the images to be displayed as a 3D image easy to view by humans (refer to, for example, Patent Literatures 1 and 2).